So. The Zombie is an adb command. It does not take any CPU or memory, but it blocks your adb from working at all. Killing it with $ kill -9 6286 does not help. $ killall -9 adb does not help either but still the Zombie adb blocks development. It is time to find adb’s parent process and go for it.
You can find the parent of the Zombie by running the following command in Terminal:

$ pstree

From the pstree you can see, that the parent of adb is java. So, time to prime your cannon and kill the parent process.

$ killall -9 java

After the parent process has been eliminated, the zombie process is also gone.